Abstract
We developed a novel type of Meju starter culture using single and combined extracts of Allium sativum (garlic clove), Nelumbo nucifera (lotus leaves), and Ginkgo biloba (ginkgo leaves) to improve the quality and functionality of Meju-based fermented products. Meju samples fermented with plant extracts (10 mg/ml) showed phenolic contents of 11.4–31.6 mg/g (gallic acid equivalents). Samples of extracts (garlic clove, lotus leaves, ginkgo leaves and their combination) fermented with Meju strongly inhibited tyrosinase, α-glucosidase, and elastase activities by 36.43–64.34%, 45.08–48.02%, and 4.52–10.90%, respectively. Specifically, ginkgo leaves extract added to fermented Meju samples at different concentrations (1% and 10%) strongly inhibited tyrosinase, α-glucosidase, and elastase activities and exhibited a potent antibacterial effect against Bacillus cereus with a significant reduction in bacterial counts compared with the effects observed for garlic clove and lotus leaf added to Meju samples. Scanning electron microscopy revealed severe morphological alterations of the B. cereus cell wall in response to ginkgo leaf extracts. Gas chromatographic mass spectroscopic analysis of plant extract-supplemented Meju samples and control Meju samples identified 113 bioactive compounds representing 98.44–99.98% total extract. The proposed approach may be useful for the development of various fermented functional foods at traditional and commercial levels.
Highlights
Korean soy foods are becoming increasingly widespread in the global market
One important problem faced in the food sector is that B. thuringiensis is closely related to B. cereus; it can be distinguished from pathogenic strains of B. cereus through its ability to produce enterotoxin
The Meju samples supplemented with plant extracts after 60 days of natural fermentation contained ash contents ranging from 11.85 ± 1.02% to 14.37 ± 1.82%
Summary
Korean soy foods are becoming increasingly widespread in the global market. Kochujang (fermented red pepper paste with soybean, flour, and glutinous rice) and fermented soybean paste products (Doenjang and Chungkukjang) were registered in the Codex Alimentarius in July 2009 and are internationally accepted foods[1]. Several attempts have been made to develop Meju manufacturing methods ensuring improved food safety by utilizing effective and beneficial microorganisms as the starter culture[4] Many synthetic antioxidants such as butylated hydroxyl anisole and butylated hydroxyl toluene are effective and are used for industrial processing. It is well known that Korean traditional soybean paste products such as Meju and Doenjang are made by natural fermentation driven by various fungi and bacteria. Meju produced in this manner may be a good growth medium for B. cereus, which is known to cause food poisoning and can affect the production of soybean paste[13]. In the present work, we focused on determining how to reduce or eliminate B. cereus counts by considering a broad spectrum in which all identified strains might exhibit pathogenic characteristics
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